The invention relates to methods and devices for processing wafer-shaped articles, such as semiconductor wafers.
Semiconductor wafers are subjected to various surface treatment processes such as etching, cleaning, polishing and material deposition. To accommodate such processes, a single wafer may be supported in relation to one or more treatment fluid nozzles by a chuck associated with a rotatable carrier, as is described for example in U.S. Pat. Nos. 4,903,717 and 5,513,668.
Such chucks include a circular series of pins positioned at the edge of the wafer. Such pins center the wafer on the chuck and limit its lateral movement. Such pins may in some designs also hold the wafer at a certain distance above the chuck. For example, in commonly-owned US Patent Pub. No. 2011/0151675 (corresponding to WO 2011/073840), the pins have a mushroom-shaped head that serves to grip the wafer edge and maintain the wafer at a fixed distance above the surface of the chuck.
As discussed in that application, certain regions of the wafer edge, including those contacted by the pins, might in some processes experience different process conditions than other regions of the wafer edge. To counteract that, it is desirable to perform a “wafer shift” during such processing, that is, to cause the wafer to rotate relative to the circular series of pins over a limited angular range.
In US 2011/0151675, wafer shift is performed by briefly accelerating or decelerating the spin chuck during processing, which in turn results in relative movement between the chuck body and the incorporated ring gear that is provided to move the pins from their radially inward service position to their radially outward loading and unloading position, owing to the inertia of the ring gear. That relative movement of the ring gear and the chuck thus causes the pins to briefly slacken their grip on the wafer edge, thereby permitting wafer shift to occur.
However, the relative movement between the wafer and the pins as occurs during conventional wafer shift causes excessive wear on the pins and significantly reduces their service life. Furthermore, prematurely worn pins do not grip the wafer evenly, and can result in increased incidence of wafer breakage at the relatively high rpm used in such spin chucks.